The present invention relates to an address assignment system for an image memory (e.g., a frame memory of a page printer) for processing image data in page units.
A conventional page printer prints character data in units of one page. When image data is transferred to a conventional page printer, the image data is temporarily stored in a frame memory. When the frame memory stores one-page image data, the one-page image data is supplied to the page printer.
A conventional page printer must deal with a large number of image data in page units, and the frame memory must therefore have a large memory capacity. For this reason, in a conventional system, a one-page frame memory is prepared, and an input from the host computer to the frame memory and an output from the frame memory to the page printer are alternately repeated. More specifically, one-page image data is transferred from the host system to the frame memory, and after the transferred data is supplied to the printer, the next one-page image data is transferred from the host system to the frame memory again. This one-page image data is transferred to the printer, and the next one-page image data is supplied from the host system to the frame memory.
In such a conventional printing control means, the next one-page image data cannot be written in the frame memory while the current one-page image data is being printed. Therefore, the next one-page image data cannot be written until the current one-page image data is completely printed. As a result, printing time is prolonged and high-speed, high-efficiency printing cannot be performed.
As shown in FIG. 1A, if a data write direction (CW) from the host system is always the same as the data output direction (Pout) to the page printer, the next one-page image data can be sequentially written in the data memory area while the current one-page image data is being transferred to the page printer. However, as shown in FIG. 1B, when the write direction (CW) is different from the read direction (Pout), the next one-page image data must be written after the current one-page image data is completely transferred to the page printer. Therefore, the overall printing time is prolonged.
In order to solve this problem, a double frame memory configuration has been proposed. Data is written in one frame memory, while the data is being transferred from the other frame memory to the page printer. However, two expensive large-capacity frame memories must be used, greatly increasing the product cost, and leading to an impractical configuration.